Antenna insulation failure detector

ABSTRACT

A device for detecting direct current flow of either polarity, in a system, usually due to corona discharge or lightning attachment. The device is unresponsive to alternating currents; and therefore, passes radio frequency signals. The device employs a means for signaling direct current flow and a means whereby it may be reset to be used again.

lJnited States Patent 1191 Truax 1 Dec. 3, 1974 [5 ANTENNA INSULATION FAILURE 3,512,149 5/1970 Pugh 340/253 R DETECTOR 3,531,790 9/1970 Staley 340/248 R 3,548,399 12/1970 Monigal.... 340/153 R Inventor: Robert Truax, 116 Fifth t, F rt 3,686,531 8/1972 Decker 340/2411 R Meyers, Fla. 33931 9 3,706,007 12/1972 Wu 340 253 R 3 31. 33 ed: Sept. 28, 1972 3,708,724 1/197 Schwc1tzer 4/1 PP 293,009 Primary Examiner-Thomas B. Habecker [52] US. Cl. 340/253 R, 324/133 [57] ABSTRACT [51] Int. Cl. G08b 21/00 A device for detectmg direct current flow of either po- [58] Fleld of Search 340/253 248 larity, in a system, usually due to corona discharge or lightning attachment. The device is unresponsive to [56] References Cite alternating currents; ancl therefore, passes radio frequency signals. The device employs a means for sig- UNITED STATES PATENTS naling direct current flow and a means whereby it may 2,586,815 2/1952 Gunn ..'340/248 C be reset to be used again. 3,115,609 12/1963 -Stanfield.. 340/253 R 3,355,729 11/1967 Dayson 340/248 R 18 Claims, 2 Drawing Flgures Body 10 f 15, 1 8 Bloc/ mg 06/28! Means Apparatus mzpea dnce 7 Test I 1 Med, ,14 LLmLeP Med;

Means I 25 //za 2'ca 07 L Medw" Re/na is 3 11 951 22 52" 7 I Siaray Means 2.91 Easel 16 firESfio/d I means 24 Voyage 7 San c6 7 Means 50 ns A 1 1 c i ANTENNA INSULATION FA LURE DETEcToR I LII from an uninsulated antenna may result from high electric field gradients,-as are present in the vicinity of a thunderstorm, or from the chargingof a structure'sup porting the antenna by tribo-electricor engine ionization means.

Antenna insulation may fail for any number of reasons. The insulation may be inadequate to prevent insulation breakdown, duringencountered electrical stresses. Vibrationmay fatigue insulating plastics. Ultraviolet radiation and other mechanisms'may age insu lation and seals. Lightning may strike and damage the antenna. Physical damage to theinsulation may occur due to mishandling, impingement of ice particles or other reasons. f r A Once the antenna insulation fails the antenna will go into corona whenever an electric field of sufficient magnitude is encountered. This corona discharge will interfere with or disrupt radio reception at frequencies toat least the UHF range. Such interference may be hazardous, especially to aeronauticaliradio navigation.

Only very sophisticated radio operators can identify most occasions of corona discharge noise interference.

Many radio signals are of the data type, where operators do not constantly, or-may not be able to, monitor reception signal quality. c

Visual inspection of antenna insulation is frequently impractical. Insulation failures are often difficult, if not impossible, to detect visually. The extremely high voltages necessary tocreate corona discharge from uninsulated antennas may be-hazardous, and are therefore seldom, if ever, used to testantennas in the field.

The present invention will detect antenna insulation failureswhencorona discharge occurs from an antenna and when antenna insulation is punctured by a light ning stroke. A I

BRIEF SUMMARY OF THE INVENTION Corona discharge results in a series of direct current pulses, of either positive or negative polarity. In the case of an antenna, these directcurrent pulses will flow through the antenna circuit to the system ground. Corona currents may vary from a microampere, or less, to several milliamperes. The corona discharge current may occur for periods of a fraction of a second to several hours.

Lightning stroke currents puncturing antenna insulation also result in a direct current flow in the antenna circuitry, which may be of either polarity. The current will flow for periods ranging from a fraction of a second to several seconds, and multiple strokes may attach during an event. Currents may range from a milliampere, or less, to 200,000 amperes or more.

' The present invention may be inserted in an antenna system between the antenna and the transmitter/- receiver. Alternating currents, as in radio frequency signals pass throughthe invention relatively unimpeded by its electronics. Direct currents as are generated by corona discharge or lightning attachment-activate this invention.

The-invention requires no source of power for its operatio'n,except the direct current energy present when corona discharge occurs-from the antenna, or when lightning attaches to the antenna.

The sensitivity of the invention is variable. Component values can beselected so as to cause operation of the monitor at a minimum direct current flow of a few microamperes, or less, to values of several amperes, if desired. The time constant of operation at a given direct current value above the minimum operating current threshold can also be pre-determined.

Upon detection of a direct current the invention may be reset without replacement of any parts.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a block diagram of the invention.

FIG. 2 is a schematic drawing of a typical embodiment of the teachings of this invention, using state of the art components.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings and FIG. 1, in particular, the monitor shown generally by number 9 is coupled by a terminal 8 between a body 10, typically an an- .tenna, and some other apparatus 18 which it is supposed to monitor, typically a radio receiver/transmitter. The monitor 9 can have withinit-a potential limiter ll designed to shunt current to a reference point 7 such as ground when the potential reaches levels that could damage the monitor 9. The monitor 9 can also have within it a blocking means 12 designed to-allow A/C currents to flow to the monitor 9 but to stop D/C current from reaching the apparatus 18. When direct current is flowing in the system, sensor 13 evaluates its amplitude and duration and, if it determines that the current is substantial, sensor 13 causes means for signaling to show a current flow. Coupled to means for signaling is remote indicating means 17, which is used to display the current information to a remote observer. In order to make the monitor 9 practicable, a

reset means 16 can be coupled to the indicating means 14 so that the monitor 9, may be used again after indicating a D/C current. A test means 15 can be included in the monitor 9, which when activated, indicates whether or not the monitor 9 is functioning properly.

FIG. 2 is a typical device built according to Applicants teachings using state-of-the-art components. Antenna 10 is coupled to monitor 9 which is coupled to radio receiver/transmitter 18. The blocking means 12 is a capacitor 20 in the radiofrequency line..Capacitor 20 is chosen so as to achieve minimum impedence, and

, to minimize other undesirable effects, at theoperating Impedance means 22 is a radio frequency isolation resister chosen to prevent undesirable radio frequency energy leakage to ground, or into the operating components of the monitor. At the same time resistor 22 must not excessively impede the flow of direct current corona discharge or lightning pulse energy from the antenna to capacitor 24 and other monitor components. Resistor 22 also functions as one of theelements in the monitor that determine the monitor operating time constant. In most embodiments, resistor 22 will vary from a few thousand ohms to many megohms.

Resistor 23 is a static drain means or bleeder resistance. This resistor provides a static current drain" to ground. It may also function to establish the minimum direct current operating point of the monitor. It can also be chosen to effect the monitor operating point. It can also be chosen toeffect the monitor operating time constant. In various embodiments resistor 23 may range in value from less than 100,000 ohms to more than 100 megohms. In other embodiments it may be omitted, in which case the leakage resistance of capacitor 24 and the electrical paths through the TRIAC 25, threshold voltage means 26 and resistor 27 provide the static current drain" path.

Capacitor 24 functions as a direct current storage means for corona discharge and lightning currents from the antenna 10. The capacitance may be varied to meet specific requirements. The monitor operating time constant is partially a function of capacitor 24. The direct current working voltage of capacitor 24 must be high enough to provide a safe margin over the voltage required to operate the monitor and the capacitance must be sufficient to store enough energy to positively actuate the indicating means 14 when that voltage is reached. Further, the insulation resistance of capacitor 24 must be such that, at the chosen operating voltage of threshold voltage means 26 and the desired current sensitivity of the overall device, the leakage current through capacitor 24 is not excessive. In practice capacitor 24 may have a capacitance ranging from a few tens of picofarads to several microfarads.

Indicating means 14 may be any of several switching, signaling or indicating devices that are dependent upon a flow of direct current, of either polarity, to operate. It may be a latching device that holds after actuation, or it may indicate each instance of current flow through the monitor circuitry. It may also indicate the value of current flow. Indicating means 14 in conjunction with storage means 24, may also be used to prevent excessive transmitter radio frequency energy from reaching and possibly damaging threshold voltage or trigger means 26 or the switch means 25. In the embodiment shown in FIG. 2, the means for signaling 14 is a latching relay or solenoid. Means for signaling 14 is chosen to operate at a voltage somewhat lower than that required to breakdown the trigger means 26 and at a current compatible with the storage means 24 and the switch means 25 chosen. The choice of a latching relay or solenoid was shown in FIG. 2, to illustrate several methods of signaling an antenna insulation failure and one method of self-testing the indication system. When operating as a latching system, provision of a reset means 16 is required if the detector is to be used again. In the embodiment shown, a mechanical indication of antenna insulation failure is incorporated. Further, a circuit to ground is closed to simultaneously provide for a remote warning indication 17, such as a light or other indicator. The grounding circuit, mechanical indication and latching operation may be verified by use of the test means 15. After such test the monitor may be reset. The actuating voltages and currents of indicating means 14 may vary widely, dependent upon the desired operating parameters of the monitor and component choices for the monitor. Voltages from a few millivolts to hundreds of volts are practical, as are currents from the microampere to hundreds of milliamperes, or even several amperes, range.

The threshold voltage means or trigger means 26 is a device for providing a signal to the control terminal 30 of the normally-open switch means 25 and in this particular embodiment a trigger input to the gate 30 of TRIAC 25. It may be any device that permits current to flow when a threshold voltage is reached. This includes, but is not limited to, avalanche diodes, ionizing gas tubes, thyratrons and spark gaps. It must also prevent current flow when some minimum voltage is reached, thereby opening the switch means 25 by gating the TRIAC 25 off, so that capacitor or storage means 24 may again charge to a potential sufficient to again operate trigger means 26. It must have characteristics such that potentials of either polarity will result in a current flow. Current capacity of threshold voltage means or trigger means 26 must be such that it can pass, without damage, any current that can flow from capacitor 24 through the indicating means or means for signaling 14 and resistor22. The threshold potential at which current flows through trigger means 26 is selected to provide a margin exceeding the minimum operating voltage of means for signaling 14.

Resistor 27 is in series with trigger means 26. Current flow through trigger means 26 creates a voltage drop across resistor 27. The resistance of resistor 27 may be any value that will result in a potential sufficient to trigger the gate-controlled silicon switch generally referred to as a TRIAC 25 by placing a signal on the control terminal or gate 30.

Capacitor 28 is used in embodiments where the current through trigger means 26 is insufficient to trigger the TRIAC 25 gate. Its value is such as is required to supply the necessary signal or gate trigger current and, in conjunction with the impedence of trigger means 26 at a time constant consistant with other time constants of the monitor.

Resistor 29 is used in embodiments where it is necessary, or desirable, to limit the TRIAC 25 gate trigger current.

The TRIAC 25 functioning as a normally-open switch presents a very high impedence to potentials of either polarity, until the control terminal or gate 30 is triggered. When the gate is triggered the impedence of the TRIAC 25 approaches a short circuit. Since both the TRIAC 25 and trigger means 26 can be in series with means for signaling 14, all, or nearly all, of the energy stored in capacitor 24 is shorted to ground through means for signaling 14. By a proper choice of component values throughout the monitor, this energy then operates the means for signaling 14. The TRIAC 25 is chosen to have a V exceeding the voltage drop across trigger means 26 and resistor 27. It is chosen to have gate trigger characteristics compatible with the characteristics of trigger means 26, resistor 27, capacitor 28, and resistor 29. The TRIAC 25 is also chosen to have current and power dissipation characteristics exceeding the energy stored in capacitor 24 and that necessary to operate means for signaling 14.

The instant invention has been shown and described herein in what is considered to be the most-practical C. indicating means, connected to said storage means, for indicating the occurrence of direct current therethrough,

D. normally open switch means, connected to said indicating means and to said reference point, for connecting said indicating means to said reference point when the switch means is closed, the switch means having a control terminal for closing the switch means in response to a signal on said control terminal, and

E. threshold voltage'means, connected to said control terminal and responsive to a potential on said storage means, for closing said normally open switch means by placing a signal on said control terminal when the potential on said storage means reaches a predetermined voltage.

2. The apparatus of claim 1 further comprising impedance means, connected between said terminal and said storage means, for preventing the flow of radio frequency energy through said threshold voltage means to said reference point.

3. The apparatus of claim 1 further comprising potential limiting means, connected between said terminal and said reference point, for shunting excessively high potentials to said reference point.

4. The apparatus of claim 1 further comprising static I drain means, connected between said terminal and said reference point, for draining static charge from said storage means.

5. The apparatus of claim 1 wherein said indicating I means is a latching relay responsive to a current flowing through said switch means.

6. The apparatus of claim 1 wherein the normally open switch means is a gate-controlled silicon switch.

7. An apparatus for monitoring a direct current between an antenna normally electrically insulated from a ground and said ground comprising:

A. a terminal insulated from ground and adapted to be connected to an antenna,

B. a capacitor connected between said terminal and ground for storing energy,

C. a relay, connected to said capacitor, for indicating the occurrence of direct current therethrough,

D. a gate controlled silicon switch, connected between said relay and ground, for connecting said v relay to ground when the silicon switch is conducting, the silicon switch having a control terminal for causing the silicon switch to conduct in response to a signal on said control terminal, and

E. threshold voltage means, connected to said control terminal and responsive to a potential on said capacitor, for causing said gate controlled silicon switch to conduct by placing a signal on said con- I trol terminal when the potential across said capacitor reaches a predetermined voltage.

8. The apparatus of claim 7 wherein the threshold voltage means is an avalanche diode.

9. The apparatus of claim 7 further comprising a resistor, connected between said terminal and said capacitor, for preventing the flow of radio frequency energy through said threshold voltage means to ground.

10. The apparatus of claim 7 further comprising a resistor connected in parallel with said capacitor between said terminal and ground for draining static charge from said capacitor.

11. The apparatus of claim 7 further comprising an avalanche diode, connected between said terminal and ground, for shunting excessively high potentials to ground.

12. The apparatus of claim 7 wherein said relay is a latching relay.

13. The apparatus of claim 12 further comprising means for resetting said latching relay to an unlatched position.

14. The apparatus of claim 7 further comprising a resistor connected between said threshold voltage means and said silicone switch control terminal for limiting the current to said control terminal.

15. The apparatus of claim 7 further comprising means for testing for correct operation of said relay.

16. The apparatus of claim 7 further comprising indicating means, remotely positioned from and connected to said relay, for remotely indicating the occurrence of a direct current therethrough.

17. An apparatus for monitoring a direct current between a body normally electrically insulated from a reference point and said reference point, said apparatus comprising:

A. a terminal, insulated from a reference point,

adapted to be connected to a body,

B. storage means, connected between said terminal and said-reference point, for storing energy,

C. indicating means, connected to said storage means and adapted for repeated operation, for repeatedly indicating the occurrence of direct current therethrough,

D. norrnally open switch means, connected between said indicating means and said reference point, for connecting said indicating means to said reference point when the switch means is closed, the switch means having a control terminal for closing the switch means in response to a signal on said control terminal, and

E. threshold voltage means, connected to said control terminal and responsive to a potential on said storage means, for closing said normally open switch means by placing a signal on said control terminal when the potential on said storage means reaches a predetermined voltage. v

18. The apparatus of claim 17 wherein said body is an antenna having insulation thereon and said storage means is adapted to store energy from a current resulting from a failure of said insulation.

UNITED STATES PATENT OFFICE CERTIFICATE CORRECTION Patent No. 3852734 Dated December 3, 1974 Inventor (5) Robert L 'I'ruax It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Inventor's address should be Fort Myers.

Column 4, line 19, the word "when should read --until--.

Column 6, line 29, the word "silicone" should read -silicon-.

Signed and sealed this 13th day of May 1975.

(SEAL) Attest:

C MARSHALL DANN RUTH C. MASON Commissioner of Patents Attesting Officer and Trademarks FORM PO-GE? (lb-G5)- 

1. An apparatus for monitoring a direct current between a body normally electrically insulated from a reference point and said reference point, said apparatus comprising: A. a terminal, insulated from a reference point, adapted to be connected to a body, B. storage means, connected between said terminal and said reference point, for storing energy, C. indicating means, connected to said storage means, for indicating the occurrence of direct current therethrough, D. normally open switch means, connected to said indicating means and to said reference point, for connecting said indicating means to said reference point when the switch means is closed, the switch means having a control terminal for closing the switch means in response to a signal on said control terminal, and E. threshold voltage means, connected to said control terminal and responsive to a potential on said storage means, for closing said normally open switch means by placing a signal on said control terminal when the potential on said storage means reaches a predetermined voltage.
 2. The apparatus of claim 1 further comprising impedance means, connected between said terminal and said storage means, for preventing the flow of radio frequency energy through said threshold voltage means to said reference point.
 3. The apparatus of claim 1 further comprising potential limiting means, connected between said terminal and said reference point, for shunting excessively high potentials to said reference point.
 4. The apparatus of claim 1 further comprising static drain means, connected between said terminal and said reference point, for draining static charge from said storage means.
 5. The apparatus of claim 1 wherein said indicating means is a latching relay responsive to a current flowing through said switch means.
 6. The apparatus of claim 1 wherein the normally open switch means is a gate-controlled silicon switch.
 7. An apparatus for monitoring a direct current between an antenna normally electrically insulated from a ground and said ground comprising: A. a terminal insulated from ground and adapted to be connected to an antenna, B. a capacitor connected between said terminal and ground for storing energy, C. a relay, connected to said capacitor, for indicating the occurrence of direct current therethrough, D. a gate controlled silicon switch, connected between said relay and ground, for connecting said relay to ground when the silicon switch is conducting, the silicon switch having a control terminal for causing the silicon switch to conduct in response to a signal on said control terminal, and E. threshold voltage means, connected to said control terminal and responsive to a potential on said capacitor, for causing said gate controlled silicon switch to conduct by placing a signal on said control terminal when the potential across said capacitor reaches a predetermined voltage.
 8. The apparatus of claim 7 wherein the threshold voltage means is an avalanche diode.
 9. The apparatus of claim 7 further comprising a resistor, connected between said terminal and said capacitor, for preventing the flow of radio frequency energy through said threshold voltage means to ground.
 10. The apparatus of claim 7 further comprising a resistor connected in parallel with said capacitor between said terminal and ground for draining static charge from said capacitor.
 11. The apparatus of claim 7 further comprising an avalanche diode, connected between said terminal and ground, for shunting excessively high potentials to ground.
 12. The apparatus of claim 7 wherein said relay is a latching relay.
 13. The apparatus of claim 12 further comprising means for resetting said latching relay to an unlatched position.
 14. The apparatus of claim 7 further comprising a resistor connected between said threshold voltage means and said silicone switch control terminal for limiting the current to said control terminal.
 15. The apparatus of claim 7 further comprising means for testing for correct operation of said relay.
 16. The apparatus of claim 7 further comprising indicating means, remotely positioned from and connected to said relay, for remotely indicating the occurrence of a direct current therethrough.
 17. An apparatus for monitoring a direct current between a body normally electrically insulated from a reference point and said reference point, said apparatus comprising: A. a terminal, insulated from a reference point, adapted to be connected to a body, B. storage means, connected between said terminal and said reference point, for storing energy, C. indicating means, connected to said storage means and adapted for repeated operation, for repeatedly indicating the occurrence of direct current therethrough, D. normally open switch means, connected between said indicating means and said reference point, for connecting said indicating means to said reference point when the switch means is closed, the switch means having a control terminal for closing the switch means in response to a signal on said control terminal, and E. threshold voltage means, cOnnected to said control terminal and responsive to a potential on said storage means, for closing said normally open switch means by placing a signal on said control terminal when the potential on said storage means reaches a predetermined voltage.
 18. The apparatus of claim 17 wherein said body is an antenna having insulation thereon and said storage means is adapted to store energy from a current resulting from a failure of said insulation. 